gistfile1.lua

    
    local print = print
	
    function permgen (a, n)
	  print ("-- permgen begin, n: " .. n)
      if n == 0 then
        printResult(a)
      else
        for i=1,n do
    
          -- put i-th element as the last one
		  local str = " --- switch " .. n .. " - " .. i .. ", value " .. a[n] .. " - " .. a[i]
		  print(str)
          a[n], a[i] = a[i], a[n]
    
          -- generate all permutations of the other elements
          permgen(a, n - 1)
    
          -- restore i-th element
          a[n], a[i] = a[i], a[n]    
        end
      end
	  
	  print("-- permgen end, n: " .. n)
    end
	
	
    function printResult (a)
      for i,v in ipairs(a) do
        io.write(v, " ")
      end
      io.write("\n")
    end
    
    -- permgen ({1,2,3,4,5}, 4)
	
    function perm (a)
      local n = table.getn(a)
	  print("-- in perm begin, n:" .. n)
      local co = coroutine.create(function () 
				permgen(a, n) 
			end)
      print("-- in perm, create co, will return with co.resume")      
      return function ()   -- iterator
        local code, res = coroutine.resume(co)
		if res ~= nil then
			print("after resume, res:" .. res)
		else
			print("after resume, nil")
		end
        return res
      end
    end
	
    for p in perm{1,2,3,4} do
      printResult(p)
    end